There is an increasing demand for synthetic materials capable of maintaining their properties at elevated temperatures and under exposure to a wide variety of chemical environments.
Of particular interest are polyimides and polyamide-imides, since these polymers are generally recognized for their outstanding physical and chemical properties. Polyimides are being marketed as varnishes, coatings for glass fibers, self-supporting films, laminating resins, and molded products such as bearings, piston rings, and the like.
U.S. Pat. Nos. which describe polyimides and polyamide-imides include 3,528,950; 3,658,764; 3,697,345; 3,781,249; 3,842,143; 3,897,395; 3,993,630; 4,035,345; 4,066,621; 4,107,153; 4,168,360; 4,302,575; 4,393,188; 4,395,514; 4,568,733; and references cited therein.
While polyimides are known to have outstanding physical and chemical properties, the problems encountered in preparing and processing polyimide prepolymers and thermoset polymers have limited their full potential.
Polyimide prepolymers in general are not readily soluble in organic solvents. In many instances the polyimide prepolymers have poor flow properties, and typically the polyimide prepolymers have high melting points and high curing temperatures. Also, the thermoset resins derived by curing of the polyimide prepolymers often tend to be brittle and lack good mechanical properties.
There is continuing research effort to develop polyimide type thermosetting prepolymers which have a desirable balance of processing properties, and which can be heat-cured to high strength composites, tough flexible films, and the like, by means of conventional equipment and procedures.
Accordingly, it is an object of this invention to provide novel thermosetting polyimide prepolymers which have desirable processing characteristics such as improved solubility and flow properties.
It is another object of this invention to provide thermosetting polyimide prepolymers which are heat-curable to high performance adhesives, coatings, films and composites with an improved combination of thermo-oxidative and mechanical properties.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.